You’re absolutely right that one of the major and most important parts of religion isn’t the philosophy at all but the community. Part of that is healthy, in that it gives people an extended family to depend on in times of need, it gives people ready friends, it gives people things to do with like-minded individuals on Sunday. I have known any number of liberal religious folk who basically continued in their religion because of the community, and frankly because they had made many of their friends through their parents at the church when they were young.
The flip side of community, or in-groups, of course, is that they do tend to produce notions of “out-groups” as well: knowing you are getting together with your friends under the green banner on Sunday means you are aware that there are many people who aren’t there with you, who may not show up every sunday. What are they off doing? And there are also people across town getting together under a blue banner ... hmmm, they can’t be all right, now can they?
(This is, absolutely, something we are all guilty of. The big problem, though, is when you think you have an infallible route to knowledge, and when you think that an eternity of afterlife depends on what you do or don’t do. That can all too easily lead to extremism).
Historically, in relatively atheistic societies like those in northern Europe, atheists don’t have atheist meetings on Sunday, so I don’t see it as such an important factor. To do that is basically (IMO) to throw in the towel and say, “Let’s become a religion too.” The Unitarian Universalists, the Quakers, the Society for Ethical Culture, even many Zen Buddhists have basically taken this route: they are (pretty much) atheists, they have meetings one day a week, they get together to talk or meditate. Funnily enough they aren’t taking the world by storm, although I for one would have little problem if they were more prominent.
My taste runs for an atheistic society (like CFI) that doesn’t try to ape religion: it doesn’t go in for rituals, even ritual meeting times. It exists to investigate, inquire and question, but little more. It is not much different from a quasi-university or museum.
But to each his own.